管内陶瓷球与粉状生物质半焦颗粒流动特性的研究
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摘要
下降管式热解液化装置是国内具有自主知识产权的反应器。在反应器内,陶瓷球作为热载体对生物质粉加热,使其发生热裂解,因此要研究下降管反应器的热解机理和工艺过程,必然涉及到颗粒在反应管内的流动特性,本研究对陶瓷球颗粒(粒径为1.5～2mm)、生物质半焦颗粒(60～80目)和二者混合颗粒在竖直管内的流动特性和速度分布进行了实验研究。
结合PIV测试系统的要求,设计制造了一套PIV颗粒流动实验台,陶瓷球和生物质半焦的喂料实验表明,漏斗形喂料装置和生物质半焦震动喂料器能够实现精确定量下料,实验可重复性强。
实验分别在抽气和自由端两种条件下,对竖直管内颗粒的速度进行了测量,并对不同抽气量下(10m~3/h,15m~3/h,20m~3/h,25m~3/h,30m~3/h,)和不同测试段的生物质半焦和陶瓷球的速度分布进行了测量和比较,进而得到颗粒在管内的速度分布曲线。
自由端时,陶瓷球和生物质半焦在管内的速度分布都呈现出中间区域大,靠近管内壁区域速度明显减小。而抽气时,管内生物质半焦中间区域的速度呈直线分布,同测试段的速度大于自由端;不同测试段生物质半焦和混合颗粒的速度分别随着抽气量的增大而增加,对于陶瓷球,抽气对其速度影响很小,但漏斗出口下端加筛网与不加筛网相比,筛网使得陶瓷球在管内的速度分布更均匀。
利用Stokes颗粒沉降速度公式计算出生物质半焦的最终沉降速度并与管内生物质半焦的最终速度进行比较。下落高度h=1200mm时,分析得出一临界抽气量(Q=11m~3/h),抽气量大于此临界值时,此测试段生物质半焦的速度大于自由端时的速度,抽气量小于此临界值时,生物质半焦的速度小于自由端的速度。抽气时生物质半焦的实测速度与管内气流的理论速度进行比较,结果表明,生物质半焦的速度取决于抽气气流的速度。
自由端时,生物质半焦在管中心的速度最终稳定在约0.8m/s,抽气时(Q=15m~3/h)约为1.2m/s。混合颗粒中生物质半焦的速度分布结果表明:混合颗粒的速度大于单独生物质半焦的速度;抽气时混合颗粒的速度大于自由端时混合颗粒的速度;抽气时单独生物质半焦的速度大于混合速度。
Down flow tube pyrolysis liquefaction apparatus is a reactor for fast pyrolysis of biomass with our own independent intellectual property rights.In the reactor,biomass powder is heated by the ceramic balls during flowing down along the tube and then pyrolyzed.It is essential to understand the flowing characteristics of particles in the down flow tube for studying the process of pyrolysis.In this study,the flowing characteristics and velocity distributions of ceramic balls(1.5~2mm in diameter), biomass-chars(60~80 mesh)and the mixture of ceramic balls and biomass chars were studied.
According the requirements for using PIV system,equipment related to the experiments were designed and fabricated.The experimental results showed that the tundish type feeding device could feed the ceramics balls and biomass chars accurately.
The velocities of the particles in the vertical duct under suction at the bottom of the tube(under suction)and with the bottom end open to the atmosphere(open end) were determined.Meanwhile,the velocity distributions of biomass chars and ceramics balls were measured and compared at different suction pump flow rates(10m~3/h, 15m~3/h,20m~3/h,25m~3/h,30m~3/h)and different heights below inlet.Finally the velocity distribution curves were obtained.
With open end condition,the velocity distribution curves of biomass chars and ceramics balls showed that velocity in the central area is bigger than that of the area near the duct-wall.Whereas,under suction condition,the velocity distribution curve of biomass-chars in central area is a flat line,and at the same height,the velocity is bigger than that of with open end condition.The velocites of biomass chars and the mixture increase as the increase of the pump flow rate,but the pump flow rate has little effect on the ceramics balls.The velocity distributions of ceramics balls are more even when a sieve type distributer is used.
The final settling velocity of biomass char calculated through the Stokes formula has been compared with final velocity of biomass-chars measured by PIV in the vertical duct.When the falling distance h=1200mm,the critical value of pump flow rate was 11m~3/h for biomass chars.When the pump flow rate is bigger than the critical value,the velocity of biomass char is bigger than that of open end.When the pump flow rate is smaller than the critical value,the velocity of biomass char is smaller than that of open end.Comparing the actual velocity of biomass-char with theoretical airflow velocity,the results indicated that under suction condition,the velocity of biomass-char was determined by the airflow velocity in the vertical duct.
The velocity of biomass char is finally stabilized at about 0.8m/s with open end condition and 1.2m/s under suction at the bottom of the tube with the suction pump flow rate of 15m~3/h.Experiments for the mixed flow of biomass-chars and ceramic balls show that the velocity of the mixture is bigger than that of biomass-char alone under the same suction condition;the velocity of the mixture under suction condition is bigger than that with open end condition;the velocity of biomass-char is bigger than that of the mixture under suction condition.
结合PIV测试系统的要求,设计制造了一套PIV颗粒流动实验台,陶瓷球和生物质半焦的喂料实验表明,漏斗形喂料装置和生物质半焦震动喂料器能够实现精确定量下料,实验可重复性强。
实验分别在抽气和自由端两种条件下,对竖直管内颗粒的速度进行了测量,并对不同抽气量下(10m~3/h,15m~3/h,20m~3/h,25m~3/h,30m~3/h,)和不同测试段的生物质半焦和陶瓷球的速度分布进行了测量和比较,进而得到颗粒在管内的速度分布曲线。
自由端时,陶瓷球和生物质半焦在管内的速度分布都呈现出中间区域大,靠近管内壁区域速度明显减小。而抽气时,管内生物质半焦中间区域的速度呈直线分布,同测试段的速度大于自由端;不同测试段生物质半焦和混合颗粒的速度分别随着抽气量的增大而增加,对于陶瓷球,抽气对其速度影响很小,但漏斗出口下端加筛网与不加筛网相比,筛网使得陶瓷球在管内的速度分布更均匀。
利用Stokes颗粒沉降速度公式计算出生物质半焦的最终沉降速度并与管内生物质半焦的最终速度进行比较。下落高度h=1200mm时,分析得出一临界抽气量(Q=11m~3/h),抽气量大于此临界值时,此测试段生物质半焦的速度大于自由端时的速度,抽气量小于此临界值时,生物质半焦的速度小于自由端的速度。抽气时生物质半焦的实测速度与管内气流的理论速度进行比较,结果表明,生物质半焦的速度取决于抽气气流的速度。
自由端时,生物质半焦在管中心的速度最终稳定在约0.8m/s,抽气时(Q=15m~3/h)约为1.2m/s。混合颗粒中生物质半焦的速度分布结果表明:混合颗粒的速度大于单独生物质半焦的速度;抽气时混合颗粒的速度大于自由端时混合颗粒的速度;抽气时单独生物质半焦的速度大于混合速度。
Down flow tube pyrolysis liquefaction apparatus is a reactor for fast pyrolysis of biomass with our own independent intellectual property rights.In the reactor,biomass powder is heated by the ceramic balls during flowing down along the tube and then pyrolyzed.It is essential to understand the flowing characteristics of particles in the down flow tube for studying the process of pyrolysis.In this study,the flowing characteristics and velocity distributions of ceramic balls(1.5~2mm in diameter), biomass-chars(60~80 mesh)and the mixture of ceramic balls and biomass chars were studied.
According the requirements for using PIV system,equipment related to the experiments were designed and fabricated.The experimental results showed that the tundish type feeding device could feed the ceramics balls and biomass chars accurately.
The velocities of the particles in the vertical duct under suction at the bottom of the tube(under suction)and with the bottom end open to the atmosphere(open end) were determined.Meanwhile,the velocity distributions of biomass chars and ceramics balls were measured and compared at different suction pump flow rates(10m~3/h, 15m~3/h,20m~3/h,25m~3/h,30m~3/h)and different heights below inlet.Finally the velocity distribution curves were obtained.
With open end condition,the velocity distribution curves of biomass chars and ceramics balls showed that velocity in the central area is bigger than that of the area near the duct-wall.Whereas,under suction condition,the velocity distribution curve of biomass-chars in central area is a flat line,and at the same height,the velocity is bigger than that of with open end condition.The velocites of biomass chars and the mixture increase as the increase of the pump flow rate,but the pump flow rate has little effect on the ceramics balls.The velocity distributions of ceramics balls are more even when a sieve type distributer is used.
The final settling velocity of biomass char calculated through the Stokes formula has been compared with final velocity of biomass-chars measured by PIV in the vertical duct.When the falling distance h=1200mm,the critical value of pump flow rate was 11m~3/h for biomass chars.When the pump flow rate is bigger than the critical value,the velocity of biomass char is bigger than that of open end.When the pump flow rate is smaller than the critical value,the velocity of biomass char is smaller than that of open end.Comparing the actual velocity of biomass-char with theoretical airflow velocity,the results indicated that under suction condition,the velocity of biomass-char was determined by the airflow velocity in the vertical duct.
The velocity of biomass char is finally stabilized at about 0.8m/s with open end condition and 1.2m/s under suction at the bottom of the tube with the suction pump flow rate of 15m~3/h.Experiments for the mixed flow of biomass-chars and ceramic balls show that the velocity of the mixture is bigger than that of biomass-char alone under the same suction condition;the velocity of the mixture under suction condition is bigger than that with open end condition;the velocity of biomass-char is bigger than that of the mixture under suction condition.
引文
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[3]倪维斗,陈贞,李政.我国能源现状及某些重要战略对策.中国能源,2008,30(12):5-9.
[4]胡敏,过静雯.环境危机与清洁能源[J].环境与可持续发展,2007,(5):49-50.
[5]李德波,柳春明,杨丽茵.2010年和2020年全国煤炭供需预测[J].电力技术经济,2007年4月,第19卷第2期:25-29.
[6]戴彦德,任东明.从我国社会经济发展所面临的能源问题看可再生能源发展的地位和作用[J].可再生能源,2005年02期(总第120期):4-8.
[7]永增.令人汗颜的进口依存度[J].中国石油石化,2007年第18期:76.
[8]Minowat,Zhen F ogi T.Liquefaction of cellbose in hot compressed water using sodium carbonate products distribution of different reaction temperature[J].Chem Eng Jpn,1997,30(1):186-190.
[9]李俊峰,王景丽,王仲颖.欧盟可再生能源的新对策及对我国的启示[J].可再生能源,2007,(5):2.
[10]周中仁,吴文良.生物质能研究现状及展望[J].农业工程学报,2005,31(12):12-15.
[11]刘荣厚,牛卫生,张大雷.生物质热化学转化技术[M].化学工业出版社,2005.1:1-3.
[12]吴创之,马隆龙.生物质能现代化利用技术[M].北京:化学工业出版社,2003
[13]包建中.中国的白色农业[M].北京:中国农业出版社,1999
[14]李俊峰.中国可再生能源技术评价[M].北京:中国环境出版社,1999
[15]邢昌风,黄泽汉.冲淡干扰布阵研究[J].舰船电子对抗,2005(1):35-37.
[16]张明.冲淡干扰对某型反舰导弹选择性的影响[J].航天电子对抗,2000(1):35-37.
[17]Reese J.,Chen R.C.,Fan L.S.,Three-dimensional particle image velocimetry for use in three-phase fluidization Exp.In fluids,Vol.19,pp.367-378,1995
[18]Meinhart C.D.,Prasad A.K.,Adrian R.J.,A Parallel Digital Processor System for Particle Imaging Velocimetry Meas.Sci.And Tech.,V61.4,pp.619-626,1993
[19]Daniel A.Steingart,JamesW.Evans.Measurements of granular in two-dimensional hoppers by particle image velocimetry.Part Ⅰ:experimental method and results[J].Chemical Engineering Science.2005,60,1043-1051.
[20]X.-L.Zhao,S.-Q.Li and G.-Q.Liu.DEM simulation of the particle dynamic in two-dimentional spouted beds[J].Powder Technology.2008,184,205-213.
[21]A.Medina,J.A.Cordova and E.Luna.Velocity field measurements in granula gravity flow in a near 2D silo[J].Physics Letters.1998,A 250,111-116.
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